I called it (weak yay) (Spoiler Episode 10) · 12:08am May 8th, 2017
Below is the short description of S7E10 from Screener.
"Starlight Glimmer is sent to solve a friendship problem between Princess Celestia and Princess Luna; when it's clear that the problem is that the royal sisters don't appreciate one another, Starlight impulsively switches their cutie marks!"
So Starlight does have the capability to switch cutie marks!
My throwaway line in Chapter 12: She even offered to show me she could even switch them as she returned them. I then, of course, firmly rejected the proposal to screw somepony over just for scientific demonstration.
doesn't get jossed!
But... does that mean she didn't learn anything about casting spells on ponies / sentient beings? Didn't she say something about not casting spells on living things during the teacup scene? I'm trying to work on her characterization to make her grow to become more sympathetic and my job isn't being made easier, eh.
Update 11/6: My ambivalence only magnified after viewing the episode. One of the alleged lessons of the episode is that Starlight should follow her inner feelings more and be bold. I doubt 'going with the guts' more are a lesson for Starlight so much as for some bookish, overly analytic pony like Twilight, for the 'spunky' Starlight seems not have a problem with being impulsive. If anything, mastering a control of feelings and emotions is something she can show to the audience as a part of character development.
The Cutie Map, a mysterious existence with shown foreknowledge (which has troubling implications on the topic of determinism, but I digress) in of itself, perhaps 'sense' or 'know' that Starlight's 'going with the guts' will go well. But it's an exception as the sisters are very accommodating for her transgression and have great sororal love for each other, and other times such impulsiveness will less likely be rewarded with a happy ending. So the literal plot device is at fault as well. The saving grace is that the spell seems to wear off by itself, but my earlier point about not tampering with other sentient beings' selves stands.
The ancient pair of royal plots should just get it over with (Heh). For Faust's sake, the two of them are thousands of years old, and their bickering somehow prompt the tree stump to direct somepony a hair of a fraction of their age to come and mediate for them!
On a more serious note, arguing over more mundane and relatable issues 'humanize' (for a lack of a better word) the royals greatly and lead to good lessons. However, if the princesses, especially Celestia, are shown to have issues with dealing with things maturely and with good judgment, their 'wise mentor' role, shall it come into play sometime in the future, might instead become tenuous and conflicting.
The description says she impulsively switches their cutie marks, meaning she did it without thinking. Personally, I don't think falling back on old habits you had for a long time when you aren't thinking clearly makes a character unsympathetic; rather, I think it's more realistic than completely abandoning behaviors you used to do all the time after only one lesson. What she does after she switches them will determine how sympathetic her character has become.
Here's my guess: the princesses will be arguing and Starlight, out of stress and panic, will switch the cutie marks. Then she'll go "I'm sorry! I'm sorry! Don't worry I can fix it!", but the princesses will ask her not to. At which point it becomes a Freaky Friday-ish plot where they spend a day or two in the other's position, where they learn more about each other and themselves.
4524326 Right, right, I'm being somewhat too harsh without the whole context, and realism and character-developing flaws are of course good points.
That being said, I'm simply always extra-sensitive towards story elements that involve shady mind alteration and mental integrity (perhaps due to my day job of signing off ethical permissions). At the risk of turning some of the stories into Author Tracts, I've tried to explain that it is something that, for the very sake of shining a better light onto the characters, should be treated less flippantly. It is censurable in its direct compromise of one's self and agency, which sets it apart from physical or property damage... for me, anyway. A lesson unlearnt and a repeating lack of awareness does disappoint me somewhat.